Three-stage propane fractionation of reduced crude oil



June 17, 1952 B. c. BENEDICT 2,600,389

THREE-STAGE PROPANE FRACTIONATION OF REDUCED CRUDE OIL Filed Dec. 25,1948 FlIIIIIIIIIIIIIIIIIIIIIIIIIII/III!'IIIIIIIIIIIIIIIIIIIIIII)LVIIIII).a

IN V EN TOR.

Y B. CBEN EDICT mn/QM ATTORNEYS Patented June 17, 1952 THREE-STAGEPROPANE FRACTIONATION OF REDUCED CRUDE OIL Bruce C. Benedict,Bartlesville, kla., assignor to Phillips Petroleum Company, acorporation of Delaware Application December 23, 1948, Serial No. 66,993

15 Claims.

This invention relates to propane-fractionation of lubricating oilstocks. In one of its more specific aspects it relates to a method forthe treatment of low asphalt-containing lubricating oil stocks for theseparation and recovery of lubricating oil fractions. In a still morespecific aspect it relates to a process for the separation and recoveryof lubricating oil fractions from crude lubricating oil stockscontaining some asphaltic material by fractionation with liquid propanewherein the asphaltic material is not precipitated and caked in the oilfractionating apparatus.

Deasphalting petroleum oils and more particularly reduced crude oilsfrom which distillate lubricating oil fractions have been removed is oldin the art. Such operations are usually carried out at temperaturesbetween about 70 and 140 F. to take advantage of the precipitatingaction of propane on the heavy asphaltic constituents of the oil. It hasalso been recognized for many years that a fractionating effect can beobtained with propane-oil mixtures at temperatures ranging from about140 F. up to the critical temperature of propane. Utilizing the uniqueproperties of liquid propane whereby increasing temperatures result inprogressive rejection of hydrocarbons in such a manner that the highermolecular Weight components and the more aromatic and naphtheniccomponents are separated first and the lighter components and moreparafiinic hydrocarbons last, a combination of low temperaturedistil1ation and solvent extraction is achieved. However, due to thedificulties involved in working at high pressures and in close proximitytothe critical temperature of propane, commercial exploitation wasunknown until quite recently.

It has been found, however, that some lowasphalt content reduced crudelubricating oils may be fractionated continuously by liquid propane at ahigh temperature and under correspondingly high pressure, while othersuch crude oil stocks can be fractionated for only short periods oftime. In this latter case it has been found that the fractionatingequipment became plugged with a deposit of asphaltic material. Thisasphaltic material had apparently been precipitated from the oil uponcontact with the high temperature liquid propane. v

An object of my invention is to devise a continuous process in which lowasphalt-containing reduced crude lubricating oil stocks are fractionatedwith propane for the separation and recovery. of lubricating oilconstituents.

Another object of my invention is to devise a method for the separationand recovery of lubricating oil constituents from such crude oil stocksby fractionation with liquid propane without the formation of hardasphaltic deposits in the propane fractionation apparatus. Still anotherobject of my invention is to devise a continuous process for theseparation and recovery of lubricating oil fractions from lowasphalt-containing reduced crude 011 stocks suitable for the manufactureof lubricating oils by liquid propane fractionation wherein theasphaltic constituents are maintained in a form which does not adhere asa hard mass to the fractionation equipment. Still other objects andadvantages of my invention will be obvious to those skilled in the artupon reading the following disclosure, which, taken with the attacheddrawing, forms a part of this specification.

In preparing to apply the above mentioned unique properties of liquidpropane to actual commercial separation of certain grades of lubricatingoil from residual stocks a hitherto unrecognized problem wasencountered. Upon treating some Mid-Continent reduced crude oil stockshaving low asphalt content with liquid propane in a countercurrentcontacting tower at a propane to oil volume ratio of about 7:1 withtemperatures ranging from about 195 F. at the top to about F. at thebottom of the tower, an SAE 40 oil was separated as overhead product. Onthe other hand, when a very similar Mid-Continent reduced crude oilstock low in asphalt content was charged to the process under the sameoperating conditions a similar fraction of lubricating oil was initiallyobtained but the column rapidly filled with a hard asphaltic material inthe stripping section, thereby making continuous operation impossible.In this second case, a third phase, that is, a semifiuid asphaltic phasewas apparently produced along with a propane-rich light oil fraction andan oil-rich solution of propane in heavy oil. Upon contacting the chargeoil with liquid propane this third phase when first formed wassufiiciently fluid to flow nearly to the bottom of the column before theascending propane had washed it sufficiently to cause it to set to ahard cake. Upon continued operation this asphalt cake builds up in thecolumn until complete closure of the column occurs.

In a study of three well known Mid-Continent reduced crude oils whichhave been long recognized as excellent sources of lubricating oil stockshard asphaltic deposits were formed in the fractionating equipment whenfractionating two of these stocks with liquid propane while the thirdwas fractionated with propane continuously and without difiiculty. Ithas also been found that some West Texas reduced crude oils can befractionated with propane while others cannot on account of asphaltdeposition. It is therefore realized that propane fractionation cannotbe universally applied to all socalled low asphalt crude lubricating oilstocks. The reason why apparently similar low-asphalt oils behave sodifferently is not known.

I have now discovered a method for the operation of a fractionatingcolumn wherein such low-asphalt lubricating oil stocks may becontinuously fractionated with propane for separation of lubricating oilfractions.

The fig-ure shows diagrammatically, partly in elevation and partly insection, one form of apparatus in which to practice the process of myinvention.

The apparatus consists essentially of three fractionating towersidentified by reference numerals I2, I6 and I8. These towers areequipped with top tower heating coils 23, 24 and 25 having pipeconnections 26, 28 and 30, respectively, for inlet and outlet of heatingfluids. Each column may be equipped with packing or contacting apparatus21 which may be merely horizontally disposed slats or it may be trays ofconventional type or any other type of packing or liquid-liquidcontacting apparatus. The main point is that this packing materialshould be such as to promote efiicient contacting between the severalliquid phases in the process. Of course, the process may be operatedwithout any contacting apparatus 21 but in such cases larger towers arerequired and liquid-liquid contactings are not especially efficient.Thus, I prefer to use some suitable type of internal contactingapparatus.

The top of tower I2 is connected with about a mid-point of tower I6 by apipe I3. Tower (6 has an overhead pipe H for product removal While pipeI9 conducts material from tower I8 to about a mid-point of tower I6.Pipes I3 and I9 are equipped with heaters 32 and 34, respectively. Fromthe bottom of tower I2 a pipe I4 conducts bottoms to about a mid-pointof tower I8 while this latter tower has a bottom outlet pipe 20 whichserves to remove one final product of the process. The centrallydisposed tower l6 has a bottom outlet connected by a pipe l5 leading toabout a mid-point of treating tower I2. Pipes I and IDA are forintroduction of feed stock into the tower I2. The towers I2, l6 and I8are each equipped with propane inlet pipes II, 22 and 21', respectively,at points near the bottom of these towers. Pipe I4 is equipped with aheater 35 while pipe I is equipped with a cooler 33. These severalheaters and coolers may be used for heating or for cooling ashereinbefore mentioned or they may be used for cooling or heating asoperating conditions of the process require.

Pilot plant propane fractionation of a Mid- Continent reduced crude oilstock of known asphalt depositing tendencies has demonstrated that apropane asphalt precipitating operation in which a very small amount ofasphalt is precipitated is not suflicient to solve the problem. Whensuch stocks are treated for removal of the .light oil content, thetreating column is quickly plugged by precipitated asphalt. Thisplugging is particularly severe when attempting to prepare an SAE 50 oilfrom certain low-asphalt crude lubricating oil stocks from which SAE 10and 20 viscosity oil fractions have already been removed and theindication is that three liquid phases are produced at the point ofentrance of the feed stock into the propane column. On the other hand,if lower temperature conditions and somewhat lower propane to oil ratiosare maintained the phase relationships are such that a third hardasphalt phase is not deposited but only high viscosity oil is separated.Under such conditions it is impossible to prepare a narrow viscosityrange lube oil stock as an overhead product which, of course, is theprimary object of propane fractionation. Due to the low propane-oilratio the bottoms product is not stripped of all the oil content desiredto be included in the overhead product. To correct this deficiency, Iprefer to operate the main extraction column under such conditions as toproduce a relatively broad overhead fraction which may containcomponents from SAE 30 to 70, inclusive. This wide viscosity rangefraction is then subject to a second fractionation under relativelysevere temperature conditions, that is, a top tower temperature of about200 with a bottom tower temperature of about 180. This high top towertemperature, coupled with a suitable propane to oil ratio, assists infractionating out an SAE 40 or 50 oil as the overhead product.

The incompletely stripped bottom product from the main fractionator mayalso be stripped of desirable oils in a third fractionating column inwhich danger of the formation of the hard asphalt deposit is avoided dueto the removal of the relatively light oils in the first column. Theoverhead oils stripped in the asphalt stripping column are introducedinto the second column which was hereinbefore described as operatingunder severe conditions on the overhead product from the first tower.The overhead fraction from column I8 (the third tower) is also passedinto the second column (I6) at a mid-point and the bottoms from thefractionation of both overhead fractions consist of relatively heavyoils and this product is returned to the first tower at about the feedplate at which point it, assists in preventing the precipitation of theasphalt phase since the asphaltic material is relatively soluble in thisheavy recycled oil.

Specific example A reduced crude oil stock of about 850 F. initialboiling point is prepared by distillation to remove SAE 10 and 20viscosity fraction. This prepared crude charge then contains all theremaining components of higher viscosity than the SAE 20 oil and is thenfractionated by means of propane to produce about an SAE 50 oil asoverhead product and a final heavy oil-asphalt product according to thefollowing sequence of steps and under the following conditions.

This prepared reduced crude oil stock is charged to the first propanecolumn I2 through the line IDA. This column has been previously filledwith liquid propane at a pressure of about 450 pounds per square inchgauge. All pressure given herein are gauge pressures and are given inpounds per square inch. The charge oil is introduced into this column ata temperature of about 150 F. Liquid propane at about F. is then pumpedinto the column through line H at a rate such that the volume ratio ofthe propane to the charge oil is about 411. At the point of introductionof the oil charge into the column,

some oily constituents dissolve in the propane while other oilyconstituents remain as an oil phase and a third phase may separate. Whena third phase separates it is a liquid phase high in asphalt content.The oil phase and this high asphalt content phase tend to descendthrough the up-flowing liquid propane. During thiscountercurrentrmovement of liquids the propane stream serves to stripthe downflowing oils of a portion of their oil content which was notpreviously dissolved by the propane at the feed plate level. In theupper or fractionating section of vessel I2, that is, the portion abovethe feed inlet, heavier and more aromatic and naphthenic portions ofdissolved oil are precipitated from the oil-propane solution bymaintaining a high temperature in the top of the column. In propanefractionation work, it is known that the higher the temperature of thepropane the less soluble are the lighter oils in propane, thus, acertain viscosity oil will be precipitated at a given temperature and byraising the temperature an oil fraction of lower viscosity isprecipitated. Thus, the top section of vessel I2 operates essentially asa refluxing section by knocking back or precipitating the highestviscosity components from the top of the tower so that components of alower viscosity may be removed as top produot. The propane to oil ratio,however, in this column I2 is such that at a top tower temperature of160 F. a relatively Wide viscosity range oil is produced. The lowpropane to oil ratio is neeessiated by the tendency of the asphaltcontent of some crude oil stocks to precipitate in the primary treatingtower.

This relatively wide viscosity range overhead fraction from the primarytower I2 due to the low top tower temperature contains a relativelylarge amount of high viscosity oils which are then removed in a secondfractionation tower I6. In column I6 this oil stock is fractionated by atemperature gradient above the feed point. On passing through line I3from the top of tower I2 to the mid-point of tower I6 this overheadproduct is heated from about 160 F. to about 190 F. so that this stockmay be introduced into tower I6 at about this temperature. This toweris, of course, previously filed with liquid. propane and propane is nowpumped into this tower through a line 22 at about one volume per volumeof charge oil to vessel I2. The propane inlet temperature to vessel I6is about 180 F. The temperature at the top of vessel I6 is maintained bythe heating coil 24 at a temperature of about 195 to 200 F. Thisrelatively high top tower temperature precipitates the highest viscosityoil components from the oilpropane solution rising from the feed pointtoward the top of the tower. This precipitated high viscosity oilsettles downward in this tower and finally accumulates as an oil phaseinthe bottom of the tower. During the settling of the precipitated oilthe upward flowing propane tends to strip the more soluble portions ofthe oil and return them to the top of the tower.

The partially stripped oil and asphalt-containing bottoms whichaccumulate in vessel I2 are withdrawn through line It and introducedinto about a mid-point of vessel I8. This bottoms product leaves vesselI2 at about 140 F. and is heated in transit by heater 35 to atemperature of about 170 prior to introduction into the treating vesselI8. Liquid propane which, of course, fills this vessel is introducedinto the bottom through line 2I and is maintained at a 6 temperature ofabout 160 F. The heating coil 25 in the top of this vessel keeps the toptower temperature at about 180 F. for refluxing purposes similar to thatdescribed in relation to the operation of vessels I2 and I6. This vesselis operated under a pressure of 55.0 pounds. The solution of heavy oilin propane which leaves the top of vessel I8 through line I9 is heatedin heater 34 prior to its introduction into about a mid-point of vesselI6. While this propane solution from the top of vessel I8 is describedas. being added to .vessel I6 at about the midpoint, it is intended tobe added thereto at about the point of introduction of the propanesolution from the top of vessel I2. These two streams need not beintroduced into vessel I6 at exactly the same point since the dissolvedoil in the two streams is different grade oil but they should be addedat points separated by preferably only a short space. The oil from pipeI9 is a relatively high viscosity oil while that in pipe I3 will have aconsiderably lower average viscosity. However, for general operationconsiderations, I prefer to add these two streams to vessel It at aboutthe same point. A heavy oil which accumulates in the base of vessel I8is withdrawn through the bottoms drawoff pipe 20 and this material maybe passed to. a propane recovery unit or to subsequent propanefractionation steps, not shown, for recovery of still higher viscosityoils if desired.

A small volume of oil-rich phase is preferably maintained in the bottomof each of the three fractionating columns. The level of each of theseseveral oil-rich phases is maintained somewhat above the points ofadditions of the propaneso that as the newly added propane reaches theliquid-liquid interfaces it will be saturated or nearly saturated withsoluble oil at the temperature conditions at that pointv in each ofthese several columns. The amount of propane introduced into column I8through line II at a temperature of about 160 F. amounts to about threevolumes of propane per volume of oil charge to the primary fractionatorI2.

In summing up the described operation, generally, vessel I2 is operatedwith a bottom temperature of -145 F., a middle point temperature of-155F., and a top temperature of -165* F. at about 400-600 poundspressure. The column I6 is operated at a bottom, a middle, and a toptemperature of -185 F., -190 F., and -210 F., respectively, at apressure of roughly 600-700 pounds. The column I8 is operated at abottom. middle. and top temperature of 155-165 F., 165-1'75 F., and175-185 F., respectively, at a pressure of roughly 500-'700 pounds. Intocolumn I2 is introduced per volume of charge oil 3 to 6 volumes ofpropane, in column I6 is introduced 1 to 3 volumes of propane, and incolumn I 8 2 to 5 volumes of propane. The overall propane to oil ratiois 6:1 to 14:1.

In the drawing is shown the line I5 connecting the bottom of vessel I6with an oil feed line I0 so that the oil phase from vessel I6 may becomemixed with charge oil so that the heavier and less paraffinichydrocarbons separated from vessel It may have ample opportunity tobecome thoroughly mixed with the charge oil before its introduction intothe primary treater I2. In this manner, these recycle oils have ampleopportunity to exert a solubilizing effect on the asphalticconstituentsof a charge oil so that these asphaltic materials will not beprecipitated as hard cake asphalt in the primary treater l2. A cooler 33may be inserted in line 15 to cool these recycle oils to the desiredtemperature of the mid-point of vessel l2 or if desired, the charge oilmay be at a temperature sufiiciently below 150 F. that the warmer oil inline 15 will make the mixture entering vessel l2 at a desired feed inlettemperature.

The propane-oil solution leaving the vessel It through the top drawofEline H may be passed to a propane recovery unit or may be passed to aunit for further fractionation, if desired, or it may be passed to arefining step, if desired. Whatever the disposal of the propane and oilsolution from pipe I! and the oil-propane solution from pipe 20, propanewill be recovered ultimately and returned to a propane run storage tank,not shown, for recycling in this system.

Contacting apparatus should preferably be used in the towers l2, l6 andi8 so that these towers may be as small as possible and yet promoteefficient contacting between propane and oil. Any type of contactingstages desired may be used provided of course they are suitable for theproblem at hand. To maintain proper temperature gradients throughout thelengths of the several treaters I2, l8 and 18 it may be desirable toinsert multiple heat exchange steps. The particular number of thesesteps, their location and temperatures maintained thereby are such as tomaintain the desired temperatures and temperature gradients.

Such auxiliary equipment as valves, pumps, pressure and temperatureregulators, flow meters, level controllers, are not shown for purposesof simplicity. The installation and operation of such equipment is wellknown in the art. It will be obvious to those skilled in the art thatmany variations in operation conditions may be made, such as slightchanges in temperatures and pressures, or even ratio of propane to oil,for accomplishing the desired and specific fractionation problem and yetremain within the intended spirit and scope of my invention.

Having disclosed my invention, I claim:

1. A process for fractionating an asphalt-containing crude lubricatingoil stock comprising maintaining a body of said oil in a first treatingzone, maintaining a body of liquid propane containing dissolved oilabove said body of oil in said first zone, said bodies meeting at acommon interface, introducing a stream of liquid propane into said bodyof oil, introducing a stream of said asphalt-containing lubricating oilstock into said body of liquid propane containing dissolved oil at amidpoint of said zone, removing propane containing dissolved oil fromthe top and asphaltcontaining oil from the bottom of said first treatingzone; maintaining a body of propane containmidpoint of said body ofpropane containing dissolved oil in said second treating zone, removingpropane containing dissolved oil from the top of said second zone andrecovering the oil as one product of the process, removing a stream ofoil rich phase from the second treating zone and introducing it intosaid first treating zone at the point of introduction of saidasphalt-containing lubricating oil stock; maintaining a body of propanecontaining dissolved oil in a third treating zone, maintaining a body ofan oil rich phase below said body of propane containing dissolved oil insaid third treating zone a said latter two bodies meeting at a commoninterface, introducing liquid propane into this latter oil rich phase,passin said removed asphalt-containing oil from said first zone into themidpoint of said body of propane containing dissolved oil in said thirdtreating zone, removing propane containing dissolved oil from top ofsaid third zone and passing this removed propane containing dissolvedoil into the body of propane containing dissolved oil in said secondtreating zone, removing oil rich phase from the bottom of said thirdtreating zone and recovering oil containing asphalt as a second productof the process.

2. The process of claim 1 wherein a higher temperature is maintained atthe top of each of the three treating zones than at the bottom of thesezones and each zone is maintained under suiiicient pressure that allcontents thereof are maintained in the liquid state.

3. The process of claim 1 wherein the temperature of the oil rich phasein the first treating zone is maintained between the limits of to F.,the temperature at the raw oil feed inlet point is maintained betweenthe limits of 145 to F., and the temperature at the point of outlet ofthe propane containing dissolved oil is maintained between the limits of155 to F., the temperature of the oil rich phase in the second treatingzone is maintained between the limits of to F., the temperature at thepoint of introduction of the streams of propane containing dissolved oilfrom the first and third zones is maintained between the limits of 185to F., and the temperature at the point of outlet of the propanecontaining dissolved oil is maintained between the limits of 190 to 210F., and the temperature of the oil rich phase in the third treating zoneis maintained between the limits of 155 to 165 F., the temperature atthe point of introduction of the stream of oil-rich phase from the firstzone is maintained between the limits of 165 to 175 F., and thetemperature at the point of outlet of the propane containing dissolvedoil in the third zone is maintained between the limits of 175 to 185 F.;the pressures maintained in the three treating zones are, respectively,450 pounds per square inch, 640 pounds per square inch and 550 poundsper square inch.

4. The process of claim 3 wherein four volumes of propane per volume ofoil charge stock is introduced into the first treating zone, one volumepropane per volume oil charge stock is introduced into the secondtreating zone and three volumes propane per volume of oil charge stockare introduced into the third treating zone. r

5. In the propane fractionation of lubricating oil constituents from lowasphalt-content reduced crude lubricating oil stocks with liquid propanewherein solid asphaltic material precipitates upon initial contact withthe propane and adheres to and plugs the fractionating apparatus in theregion adjacent and below the raw feed entry point, a process forcontinuously carrying out this fractionation operation withoutprecipitating said asphalt and plugging said apparatus comprisingmaintaining a body of said oil in a first treating zone, maintaining abody of liquid propane containing dissolved oil above said body of oilin said first zone, said bodies meeting at a common interface,introducing a stream of liquid propane into said body of oil,introducing a stream of said low asphalt-content reduced crudelubricating oil stock into said body of liquid propane containingdissolved oil at a midpoint of said body of propane containing dissolvedoil, removing propane containing dissolved oil from the top andasphalt-containing oil from the bottom of said first treating zone;maintaining a body of propane containing dissolved oil in a secondtreating zone at a temperature higher than the temperature of the bodyof propane containing dissolved oil in said first zone, maintaining abody of an oil rich phase below said body of propane containingdissolved oil in said second treating zone, said latter two bodiesmeeting at a common interface, introducing liquid propane into thislatter oil rich phase, passing said removed propane containing dissolvedoil from said first treating zone into the midpoint of said body ofpropane containing dissolved oil in said second treating zone, removingpropane containing dissolved oil from the top of said second zone andrecovering the oil as one product of the process, removing a stream ofoil rich phase from the second treating zone and introducing it intosaid first treating zone at the point of introduction of saidasphalt-containing lubricating oil stock; maintaining a body of propanecontaining dissolved oil in a third treating zone, maintaining a body ofan oil rich phase below said body of propane containing dissolved oil insaid third treating zone, said latter two bodies meeting at a commoninterface, introducing liquid propane into this latter oil rich phase,passing said removed asphalt-containing oil from said first zone intothe midpoint of said body of propane containing dissolved oil in saidthird treating zone, removing propane containing dissolved oil from topof said third zone and passing this removed propane containing dissolvedoil into the body of propane containing dissolved oil in said secondtreating zone, removing oil rich phase from the bottom of said thirdtreating zone and recovering oil containing asphalt as a second productof the process.

6. The process of claim wherein a higher temperature is maintained atthe top of each of the three treating zones than at the bottom of thesezones and each zone is maintained under suificient pressure that allcontents thereof are maintained in the liquid state.

'7. The process of claim 5 wherein the temperature of the oil rich phasein the first treating zone is maintained between the limits of 120 to145 the temperature at the raw oil feed inlet point is maintainedbetween the limits of 145 to 155 F.. and the temperature at the point ofoutlet of the propane containing dissolved oil is maintained between thelimits of 155 to 165 F., the temperature of the oil rich phase in thesecond treating zone is maintained between the limits of 175 to 185 F.,the temperature at the point of introduction of the streams of propanecontaining dissolved oil from the first and third zones is maintainedbetween the limits of 185 to 190 F'., and the temperature at the pointof outlet of the propane containing dissolved oil is maintained betweenthe limits of 190 to 210 F., and the temperature of the oil rich phasein the third treating zone is maintained between the limits of 155 to165 F., the temperature at the point of introduction of the stream ofoil-rich phase from the first zone is maintained between the limits of165 to 175 F., and. the temperature at the point of outlet of thepropane containing dissolved oil in the third zone is maintained betweenthe limits of to F.; the pressures maintained in the three treatingzones are, respec tively, 450 pounds per square inch, 640 pounds persquare inch and 550 pounds per square inch.

8. The process of claim 5 wherein four volumes of propane per volume ofoil charge stockis introduced into the first treating zone, one volumepropane per volume oil charge stock is introduced into the secondtreating zone and three volumes propane per volume of oil charge stool:are introduced into the third treating zone.

9. In the propane fractionation of lubricating oil constituents from lowasphalt-content reduced crude lubricating oil stocks with liquid propanewherein solid asphaltic material precipitates upon initial contact withthe propane under propane fractionation conditions and adheres to andplugs the fractionating apparatus in the region adjacent and below theraw feed entry point, a process for continuously carrying out thisfractionation operation without precipitating said asphalt and pluggingsaid apparatus comprising maintaining a body of oil in a first treatingzone, mantaining a body of liquid propane containing dissolved oil abovesaid body of oil in said first zone, said bodies meeting at a commoninterface, introducing a stream of liquid propane into said body of oil,introducing a stream of said reduced crude lubricating oilstock'containing .some of said asphalt into said body of liquid propanecontaining dissolved oil at an intermediate point of said zone, removingpropane containing dissolved oil from the top and oil containing asphaltin solution from the bottom of said first treating zone and recoveringoil containing asphalt in solution from said removed bottoms as oneproduct of the process; maintaining a body of propane containingdissolved oil in a second treating zone at a temperature higher than thetemperature, of the body of propane containing dissolved oil in saidfirst zone, maintaining a body of an oil rich phase below said body ofpropane containing dissolved oil in said second zone, said two bodiesmeeting at a common interface, introducing liquid propane into thislatter oil rich phase, passing said removed propane containing dissolvedoil from said first treating zone into an intermediate point of saidbody of propane containing dissolved oil in said second treating zone,removing propane containing dissolved oil from the top of said secondzone and recovering the oil as a. second product of the process,removing a stream of an oil phase comprising aromatic and naphthenicconstituents from the bottom of said second zone and passing at least aportion of this stream into the first zone at the reduced crude oil feedinlet level thereof.

10. The process of claim 9 wherein the pressures in both treating zonesare sufficiently high as to maintain the propane in the liquid phase.

11. The process of claim 9 wherein the temperature from saidintermediate point to the bottom of the first zone is maintainedconstant, and the temperature from the midpoint to the top of said firstzone is maintained progressively higher than at the bottom of said firstzone; and an increasing temperature gradient is maintained from thebottom to the top of the second zone; and both zones are maintained atsufliciently high pressures that the propane therein exists in theliquid phase.

12. The process of claim 9 wherein the temperature from the bottom ofthe second zone to estates the top thereof progressively increases from180 F. to 200 F., and both zones are maintained at sufliciently highpressures that the propane therein exists in the liquid phase.

13. The process of claim 9 wherein six volumes of liquid propane pervolume of said low asphaltcontaining crude lubricating oil feed stockare introduced into the oil rich, phase of the first treatingzone andtwo volumes of liquid propane per volumeof said low asphalt-containingcrude lubricating oil feed stock are introduced into the sc'rmd treatingzone; and wherein the temperature from the bottom of the second zone tothe top thereof progressively increases from 180 F. to 200 F., and bothzones'are maintained at sufficiently high pressures that the propanetherein eirists in the liquid phase.

-14. The process of claim 9 wherein from 3 to 6 volumes of liquidpropane per volume of said low asphalt-containing crude lubricating oilfeed stock are introduced into the oil-rich phase of the first treatingzone and from 1 to 3 volumes of liquid propane per volume of said lowasphaltcontaining crude lubricating oil feed stock are introduced intothe second treating zone; and wherein the temperature from the bottom ofthe second zone to the top thereof progressively increases from 180 F.to a temperature within the limits of 195 to 210 F. 15. In the propanefractionation of lubricating oil constituents from low asphalt-contentreduced crude lubricating oil stocks with liquid propane wherein solidasphaltic material precipitates upon initial contact with the propaneunder propane fractionation conditions and adheres to and plugs thefractionating apparatus in the region adjacent and below the raw feedentry point, a process for continuously carrying out this fractionationoperation without precipitating said asphalt and plugging said apparatuswith deposited asphalt comprising maintaining a body of oil in a firstfractionation zone, maintaining a body of liquid propane containingdissolved oil above said body of oil in said first zone, said 12 bodiesmeeting at a common interface, introducing a stream of liquid propaneinto said body of oil, introducing a stream of said reduced crudelubricating oil stock containing said asphalt into said body of liquidpropane containing dissolved oil at an intermediate point thereof,removing propane containing dissolved oil from the top and oilcontaining asphalt in solution from thebottom of said firstfractionation zone and recovering oil containing asphalt in solutionfrom said removed bottoms as one product of the process; maintaining abody of liquid propane containing dissolved oil in a secondfractionation zone, maintaining a body of an oil rich phase below saidbody of propane containing dissolved oil in said second zone, said twobodies meeting at a common interface, introducing liquid propane intothis latter oil rich phase, passing said removed propane containingdissolved oil from said first fractionation zone into an intermediatepoint of said body of propane containing dissolved oil in said secondfractionation zone, removing propane containing dissolved oil from thetop of said second zone and recovering the oil as a second prodnot ofthe process, removing a stream of an oil phase comprising aromatic andnaphthenic constituents from the bottom of said second zone and passingat least a portion of this stream into the first zone at the reducedcrude oil inlet level thereof.

BRUCE C. BENEDICT.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,079,886 Voorhees May 11, 19372,079,911 Keith et al May 11, 1937 2,091,078 McKittrick et al. Aug. 24,1937 2,198,388 Landau Apr. 23, 1940 2,367,671 Dickinson et a1. Jan. 23,1945 2,500,757 Kiersted Mar. 14, 1950

1. A PROCESS FOR FRACTIONATING AN ASPHALT-CONTAINING CRUDE LUBRICATINGOIL STOCK COMPRISING MAINTAINING A BODY OF SAID OIL IN A FIRST TREATINGZONE, MAINTAINING A BODY OF LIQUID PROPANE CONTAINING DISSOLVED OILABOVE SAID BODY OF OIL IN SAID FIRST ZONE, SAID BODIES MEETING AT ACOMMON INTERFACE, INTRODUCING A STEAM OF LIQUID PROPANE INTO SAID BODYOF OIL, INTRODUCING A STREAM OF SAID ASPHALT-CONTAINING LUBRICATING OILSTOCK INTO SAID BODY OF LIQUID PROPANE CONTAINING DISSOLVED OIL AT AMIDPOINT OF SAID ZONE, REMOVING PROPANE CONTAINING DISSOLVED OIL FROMTHE TOP AND ASPHALTCONTAINING OIL FROM THE BOTTOM OF SAID FIRST TREATINGZONE; MAINTAINING A BODY OF PROPANE CONTAINING DISSOLVED OIL IN A SECONDTREATING ZONE AT A TEMPERATURE HIGHER THAN THE TEMPERATURE OF THE BODYOF PROPANE CONTAINING DISSOLVED OIL IN SAID FIRST ZONE, MAINTAINING ABODY OF AN OIL RICH PHASE BELOW SAID BODY OF PROPANE CONTAININGDISSOLVED OIL IN SAID SECOND TREATING ZONE, SAID LATTER TWO BODIESMEETING AT A COMMON INTERFACE, INTRODUCING LIQUID PROPANE INTO THISLATTER OIL RICH PHASE, PASSING SAID REMOVED PROPANE CONTAINING DISSOLVEDOIL FROM SAID FRIST TREATING ZONE INTO THE MIDPOINT OF SAID BODY OFPROPANE CONTAINING DISSOLVED OIL IN SAID SECOND TREATING ZONE, REMOVINGPROPANE CONTAINING DISSOLVED OIL FROM THE TOP OF SAID SECOND ZONE ANDRECOVERING THE OIL AS ONE